Enhanced dispersion and the reactivity of atomically thin Rh layers supported by molybdenum oxide films
The behavior of rhodium layers deposited on oxidized, 0.15-20.0 ML thick Mo films formed on a nearly stoichiometric TiO<inf>2</inf>(110) single crystal was characterized by AES, TPD and work function (WF) measurements. The oxidation of 0.15-2.7 ML thick Mo deposits was performed via the...
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| Format: | Article |
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Elsevier
2015
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| Series: | SURFACE SCIENCE
641 |
| doi: | 10.1016/j.susc.2015.05.008 |
| mtmt: | 2958256 |
| Online Access: | http://publicatio.bibl.u-szeged.hu/9849 |
| Summary: | The behavior of rhodium layers deposited on oxidized, 0.15-20.0 ML thick Mo films formed on a nearly stoichiometric TiO<inf>2</inf>(110) single crystal was characterized by AES, TPD and work function (WF) measurements. The oxidation of 0.15-2.7 ML thick Mo deposits was performed via the redox reaction with the titania support at 1000 K. Molybdenum oxide supports of MoO<inf>3</inf> and MoO<inf>2</inf> surface composition were formed by the oxidation of 20 ML thick Mo multilayers by O<inf>2</inf> at 650 K and 1000 K, respectively. Rh grows in a layer-by-layer fashion on a mixed titanium-molybdenum oxide produced in the reaction between titania and 0.15 ML Mo, corresponding to a considerably enhanced dispersion of rhodium as compared with that on the clean TiO<inf>2</inf>(110). The surface reactivity of Rh layers supported by molybdenum oxides as a function of pre-annealing temperature was followed by carbon monoxide adsorption-desorption cycles. The CO uptake of a 0.4 ML thick Rh film formed on the MoO<inf>3</inf> support was strongly suppressed at 300 K, indicating the encapsulation of rhodium with MoO<inf>X</inf> species of low surface free energy. The CO adsorption capability of rhodium particles supported by both MoO<inf>3</inf> and MoO<inf>2</inf> layers was eliminated due to pre-annealing at 600 K, related to the extended decoration of metal particles by MoO<inf>X</inf> moiety. The encapsulation of the rhodium films proceeded above 600 K on both supports, and annealing to 1000 K resulted in nearly equal WF values, indicating the formation of MoO<inf>X</inf> overlayers of similar surface composition close to MoO<inf>2</inf>. AES depth profiles revealed that the 0.4 ML thick Rh deposits covered by MoO<inf>X</inf> at 1000 K preserved their island structure. © 2015 Elsevier B.V. All rights reserved. |
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| Physical Description: | 60-67 |
| ISSN: | 0039-6028 |